I. Field
The present disclosure relates generally to electronics, and more specifically to a filter.
II. Background
In a wireless communication system, a transmitter may digitally process (e.g., encode and modulate) digital data to generate output samples. The transmitter may further condition (e.g., convert to analog, amplify, filter, and frequency upconvert) the output samples to generate a radio frequency (RF) modulated signal. The transmitter may then transmit the RF modulated signal via a wireless channel to a receiver.
The receiver may receive the transmitted RF signal and perform the complementary processing on the received RF signal. The receiver may condition (e.g., amplify, frequency downconvert, filter, and digitize) the received RF signal to obtain input samples. The receiver may further process (e.g., demodulate and decode) the input samples to recover the transmitted data.
The receiver may employ one or more analog lowpass filters to perform filtering. Each analog lowpass filter may be implemented with resistors and capacitors to obtain a desired filter transfer function. The resistors and capacitors may have high tolerances (especially when implemented on an integrated circuit), which may result in poor filter precision. Calibration circuits may be used to determine an RC time constant of the resistors and capacitors and to tune the resistors and/or capacitors to obtain the desired filter transfer function. The calibration circuits and extra resistors and/or capacitors to compensate for component tolerances would increase the die area of the analog lowpass filter and also increase calibration time of the receiver. Furthermore, the dynamic range of an analog-to-digital converter (ADC) in the receiver may need to be larger to account for residual component tolerance and to allow for the worst case filter attenuation. A lowpass filter that can avoid these shortcomings of the analog lowpass filter may be highly desirable.